1. Field of the Invention
The invention relates to an electric connector to be equipped in a circuit board and used for electrically connecting to a signal-transmission medium such as FPC (Flexible Printed Circuit) and FFC (Flexible Flat Cable). The invention further relates to a lock device to be used in an electric connector.
2. Description of the Related Art
FIG. 1 is a cross-sectional view of a conventional electric connector used for electrically connecting to a signal-transmission medium such as FPC and FFC.
As illustrated in FIG. 1, the conventional electric connector 150 includes a housing 153 having a groove 152 into which a signal-transmission medium 151 such as FPC and FFC is inserted at opposite edges thereof, and a lock device 154 including a lock 154a for locking the signal-transmission medium 151 at the groove 152 and allowing the signal-transmission medium 151 to be released out of the groove 152. The locker 154a is designed to move up beyond and move down below a lower inner surface 152a of the groove 152.
The lock device 154 is formed of an elastic material. The locker 154a is energized towards an upper inner surface 152b facing the lower inner surface 152a. 
The signal-transmission medium 151 is formed at each of side edges thereof with a cut-out 151a. Inserting the signal-transmission medium 151 into the groove 152 in a direction indicated with an arrow X, the signal-transmission medium 151 makes contact at a lower surface 151b thereof with the locker 154a, and pushes the locker 154a down. When the cut-out 151a reaches a position above the locker 154a, the locker 154a moves up by virtue of an elastic force of the lock device 154 to thereby fit into the cut-out 151a. Thus, the signal-transmission medium 151 is fixed in the groove 152.
There have been suggested various electric connectors apart from the above-mentioned electric connector 150. As a conventional electric connector related to the electric connector in accordance with the present invention, Japanese Patent Application Publication No. 2008-153059 has suggested “a connector”, for instance.
As illustrated in FIG. 1, in the conventional electric connector 150, the locker 154a upwardly protrudes beyond the lower inner surface 152a of the groove 152 by a height necessary for engaging to the cut-out 151a. Consequently, if a thickness 151t of the signal-transmission medium 151 inserted into the groove 152 is smaller than a distance 152c between the lower inner surface 152a and the upper inner surface 152b of the groove 152, there is generated a space G between the signal-transmission medium 151 and the upper inner surface 152b of the groove 152. Thus, if the signal-transmission medium 151 moves upwardly, a length by which the locker 154a is engaged to the cut-out 151a of the signal-transmission medium 151 is reduced. Such a length varies in dependence on a variance of the thickness 151t of the signal-transmission medium 151. Accordingly, if such a length were small, the locker 154a makes unstable engagement with the cut-out 151a, resulting in reduction in contact reliability between the electric connector 150 and the signal-transmission medium 151.
Though the “connector” suggested in the above-identified Publication is designed to have a countermeasure for avoiding the reduction in contact reliability, the reduction in contact reliability in the conventional electric connector 150 illustrated in FIG. 1 cannot be prevented by the above-identified Publication.